Liquids of the liquified petroleum gas type, such as propane, butane, and the like (often referred to generally as LPG), are commonly used for purposes such as residential or industrial heating, or for powering internal combustion engines on industrial vehicles such as lift trucks (i.e, fork lifts). The LPG is typically stored as a liquid under pressure in a pressurized tank or cylinder. A liquid level gauge may be provided on the tank for measuring the level of the liquid in the tank. In some applications such as lift trucks, the LPG cylinders are oriented horizontally while in use on the vehicle but are stored vertically when removed for refueling. In such applications, a liquid level gauge which can measure liquid levels in both orientations is desirable.
Liquid level gauges for measuring the level of a liquid such as LPG inside a pressurized tank are disclosed in U.S. Pat. Nos. 2,992,560 and 3,688,795. These patents disclose float-type liquid level gauges that utilize a pivoting float arm having a position which is responsive to the liquid level inside the tank. The float arm is connected to a rotatable shaft by means of a geared mechanism, and the shaft is magnetically coupled to an external liquid level indicator. A change in liquid level causes the float arm to rotate the shaft, and the magnetic coupling then rotates the external indicator without requiring a direct physical connection. Thus, the possibility of volatile liquid or vapor leaking through the mechanism is eliminated.
While useful, the previously disclosed float-type gauges have several drawbacks. First, due to the low density of LPG, the heavy-walled hollow float used to resist the pressure in the tank has insufficient buoyancy to float without a counterweight to balance the float arm. Such counterweights are typically discrete components which add to the manufacture and assembly expense of the gauge, and their size often increases the difficulty in installing the gauge through the narrow opening of the tank or cylinder. For example, on many lift truck cylinders and tanks for recreational vehicles (RVs), the in-tank parts of the level gauge must fit through a 3/4" opening. A need therefore exists, for a liquid level gauge which does not require a counterweight, or where the counterweight is a small, integral part of another component.
Further, the design of previously disclosed float type gauges required the use of a large number of small discrete secondary components, such as gears, axles, bearings, and fasteners, in addition to the primary components, such as gauge head, support arm, drive shaft, magnet, float arm, and float. These discrete secondary components greatly increase the complexity of previously disclosed float type gauges and the expenses associated with the design, production and stocking of these typically small components increased the cost of the finished gauge. A need therefore exists, for a liquid level gauge which does not require a significant number of discrete secondary components.
Similarly, the complex design of previously disclosed float type gauges necessitates the use of skilled workers for their assembly. For example, the previously disclosed tubular support arms required that the magnet drive shaft be inserted through the end of the support arm and held in position by a discrete bearings or end caps which were themselves installed within or onto the support arm as one or more separate assembly operations. The large number of separate assembly operations and the need for skilled workers to perform these operations increases the cost of the finished gauge. A need therefore exists, for a liquid level gauge which does not require skilled workers for assembly and minimizes the number of separate assembly operations.